This invention relates generally to linear actuator devices. The invention relates more particularly to an improved form of electromagnetic linear actuator.
One form of linear actuator comprises an electromechanically operated device which is mechanically coupled to a body to be acted upon and which imparts rectilinear motion to the body. Various systems have operating requirements wherein the body must be rapidly displaced by the actuator over a relatively short distance. For example, a high storage capacity, random access magnetic storage memory which is frequently used with computing systems is a magnetic disk file memory. This memory generally includes a plurality of aligned, spaced-apart disks each having a magnetic medium deposited on its opposite surfaces. Bits of binary information are stored in the form of residual magnetic flux on circular tracks which are located at different radial sectors or zones of a disk. The binary information is stored by rotating the disks and exciting a magnetic head which is positioned adjacent a moving surface of a rotating disk. Readout of data is similarly provided by positioning the head adjacent the moving surface.
Access to stored data at a particular storage track on a disk is provided by an accessor means. The accessor means generally includes a carriage and a magnetic head support arm which transports a magnetic head in a radial direction with respect to a surface of the disk to a selected track location. Since short access time is an important characteristic of a memory device, the head is rapidly accelerated between different storage locations. The head, for example, is expected to move a distance of three or 4 inches in milliseconds. In practice, one or more heads are associated with each disk and are mounted on one or more support arms. The support arms, which are in some arrangements mechanically ganged together, receive motive power for radial transport of the heads from an electromagnetic linear actuator through the carriage. The present invention is directed toward an improved electromagnetic linear actuator arrangement.
A known form of electromagnetic linear actuator which is also referred to in this art as a voice coil comprises a magnetic circuit provided by a permanent magnet having an air gap and a winding or coil which is mounted on a form and which is positioned in the air gap. Electrical energization of the winding establishes a field which reacts with the magnetic circuit and causes rectilinear motion of the form. The form is mechanically coupled to the carriage which in turn is secured to the magnetic head supporting arm. As the winding is electrically energized, it causes rectilinear motion of the form thereby rapidly transporting the heads in a radial direction between different memory locations on the disk. By controlled energization of the winding, a magnetic head is aligned with a preselected data track for recording or recovery of information.
A disk file memory device includes several stacks of aligned, spaced apart disks. Each stack may include on the order of twenty to thirty disks. Various mechanical arrangements have been employed in order to provide access to any track address at any one disk in a file memory. In one arrangement, a separate electromagnetic linear actuator is provided for each disk. Alternatively the number of actuators has been reduced through the mechanical ganging of accessors in combination with electronic selection of one of a number of mechanically accessed disks. In each of these arrangements, the actuator and accessor are preferably positioned in relatively close proximity to the disk file for reducing the complexity of the mechanical arrangement employed. This relatively close spacing as well as the close spacing of disks in a file memory render the size, configuration and arrangement of the various accessor components important. In this regard, the means for providing a stationary magnetic circuit of the electromagnetic linear actuator can be bulky, relatively heavy, and difficult to position in the limited space available adjacent a disk file. For example, the actuator may be required to displace bodies having a total weight of about three pounds. The necessary speed of reaction and length of stroke requires forces which can only be provided by a relatively large permanent magnet. Stationary magnetic circuits weighing seventy pounds are common. It is therefore desirable to provide an electromagnetic linear accelerator of relatively reduced size and weight.
Prior arrangements directed to reducing the overall size of an actuator have utilized at least two windings with common magnetic circuit components. While the prior arrangement has reduced to some extent the size of the required magnetic circuit, it has also resulted in an interaction between the windings and the magnetic circuit necessitating the use of mechanical compensating means for equilibrating the motion of the windings and thus adding to the complexity of the actuator.
Accordingly, it is an object of the present invention to provide an improved electromagnetic linear actuator.
Another object of the invention is to provide an improved electromagnetic linear actuator for a disk file memory.
Another object of the invention is to provide an improved electromagnetic linear actuator having a magnetic circuit adapted for operation with a plurality of actuating windings.
Another object of the invention is to provide a multi-winding electromagnetic linear actuator of relatively reduced size and complexity.
Another object of the invention is to provide an electromagnetic linear actuator of modular construction which facilitates expansion of the actuator to receive additional windings.
A further object of the invention is to provide a multi-winding electromagnetic linear actuator in which the windings are adapted to be displaced in opposite directions.
Another object of the invention is to provide an electromagnetic linear actuator arrangement having a plurality of windings wherein one winding operates to provide coarse positioning of a body and a second winding operates to provide fine or vernier positioning of the body.